Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760597Ab3GaUpk (ORCPT ); Wed, 31 Jul 2013 16:45:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:61951 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755143Ab3GaUpj (ORCPT ); Wed, 31 Jul 2013 16:45:39 -0400 Date: Wed, 31 Jul 2013 22:40:03 +0200 From: Oleg Nesterov To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Masami Hiramatsu , "zhangwei(Jovi)" , Jiri Olsa , Peter Zijlstra , Arnaldo Carvalho de Melo , Srikar Dronamraju , Frederic Weisbecker , Ingo Molnar , Andrew Morton Subject: Re: [RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe event files are open Message-ID: <20130731204003.GA30188@redhat.com> References: <20130704033347.807661713@goodmis.org> <20130704034038.819592356@goodmis.org> <1375300192.5418.17.camel@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1375300192.5418.17.camel@gandalf.local.home> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1652 Lines: 48 On 07/31, Steven Rostedt wrote: > > On Wed, 2013-07-03 at 23:33 -0400, Steven Rostedt wrote: > > The above will corrupt the kprobe system, as the write to the enable > > file will happen after the kprobe was deleted. > > Oleg, > > The above no longer triggers the bug due to your changes. The race is > much tighter now Yes, the changelog should be updated... > and requires a process with the enable file opened and > races with a write to enable it where the removal of the trace file > checks the trace disabled, sees that it is, continues, but then the > write enables it just as it gets deleted. This should be fine. Either event_remove() path takes event_mutex first and then ->write() fails, or ftrace_event_enable_disable() actually disables this even successfully. > Do you know of a way to trigger this bug? I'll try to think more tomorrow, but most probably no. The race is unlikely. We need perf_trace_event_init() or ":enable_event:this-event" right before trace_remove_event_call() takes the mutex. And right after the caller (kprobes) checks "disabled". > Hmm, what happens without this patch now? If it is active, and we delete > it? It will call back into the kprobes and access a tracepoint that does > not exist? Would this cause a crash? I think yes, the crash is possible. perf or FL_SOFT_MODE, this call/file has the external references, and we are going to free it. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/